The present invention relates to making parts out of composite material, and more particularly to making reinforcing fiber structures for such parts.
A particular field of application of the invention lies in making parts of structural composite material, i.e. parts having a fiber reinforcing structure that is densified by a matrix. Composite materials make it possible to fabricate parts that present overall weight that is less than that of the same parts when made of metal.
In the context of making fiber structures by multilayer weaving so as to produce the fiber reinforcement for a composite material part, such as a blade for an aeroengine, it is necessary during weaving of the structure to withdraw yarns both in the warp direction and in the weft direction in order to match reductions in the thickness of the part, e.g. in the fastening or in the trailing edge of the blade, so as to obtain a fiber preform that presents the quasi-final shape and dimensions of the blade (i.e. that presents its “net shape”).
In the portions of the fiber structure that have a large number of layers of yarns, withdrawing yarns has little influence on varying the density of the fibers, which density remains relatively constant. Nevertheless, once the number of layers decreases significantly, e.g. when there remain only four or fewer layers of weft yarns or of warp yarns, then the variation in fiber density becomes too great when another layer of yarns is withdrawn.